For the high-speed LSI for the recent wireless LAN, such as Bluetooth, the balanced-mode signals are in most cases produced in order to increase the signal noise margin.
As the wireless circuit generally employs an unbalanced circuit, however, the balun (balanced unbalanced conversion circuit) constitutes an essential element for performing this conversion.
The balun may comprise two branch circuits, that is, a ¼-wavelength line and a ¾-wavelength line.
When the balun includes the ¼-wavelength line and ¾-wavelegth line, however, they have a different line length. Thus, even if a frequency can have a phase of 180 degrees with regard to the central frequency, the phase shift may be increased if the frequency is shifted within a band.
In view of the above fact, it is an object of the present invention to provide a balun in which the phase shift can be reduced significantly.